In a power conditioner or the like that is disposed between a power generator such as solar photovoltaic power generator or the like and a system power supply (system), a fan control unit containing an air-cooling fan and a control section thereof is provided, together with an inverter. While in the power conditioner, DC power generated by the power generator is converted into AC power and then the AC power is outputted to the system, the power generated usually varies in time. In particular, in a case where the power generator is a solar photovoltaic power generator, the power generated changes considerably, depending on weather conditions and time of day. Since heat generated by the internal inverter or the like changes when the power generated varies, in a case where an air-cooling fan is kept turned on all the time, the air-cooling by the fan becomes excessive during the time when the heat generated is little, which results in wasteful power consumption.
Then, there has become known a prior art apparatus in which the number of air-cooling devices that are turned on is controlled among a plurality of the air-cooling devices provided, depending on the power generated, thereby achieving an adequate cooling capability that depends on the heat generated (Patent Literature 1).